This invention relates to a filter punch construction and to a system utilizing the filter punch for collecting sample deposited on a filter.
Test plates for in vitro analysis which contain a multiplicity of individual wells or reaction chambers are commonly known laboratory tools. Such devices have been employed for a wide variety of purposes and assays as exemplified by U.S. Pat. Nos. 3,694,464; 4,304,865; 4,276,048; 4,154,795; 4,427,415; 4,526,690 and Re 30,562. Microporous membrane filters and filtration devices containing such microporous membranes have been especially useful with many of the recently developed cell and tissue culture techniques and assays, particularly those in the field of virology and immunology, wherein the material of interest is retained by the filter. Typically, a ninety-six well filtration plate is used to conduct multiple assays simultaneously, some steps of which last several hours prior to performing filtration. Subsequent to filtration, it is common practice to utilize a die-punch having a flat face which is inserted into the well and through the filter paper bearing the retentate in order to direct the filter paper and retentate from the well into a vial for subsequent testing. This system has two major problems. First, many times only a portion of the filter paper circumference is sheared and the filter disc remains attached to the well. Secondly, the flat face of the punch tends to remove some of the retentate from the filter paper so that the subsequent testing is inaccurate. An alternative system utilizes a hollow tube as a punch to minimize the contact face of the punch and reduce the amount of sample accidentally transferred to the punch. In another system, the filter is scored about its circumference in order to facilitate subsequent punching. This system is undesirable since accidental rupturing of the filter paper along the scoring can occur during filtration.
The filter punch disclosed in U.S. Pat. No. 4,974,462, while a great improvement over previous punching means, does not provide 100% complete filter removal with fragile membranes. This is because the filter periphery does not separate everywhere simultaneously. Sometimes, the unbroken portion of the periphery imposes a side force upon the filter section. These side forces can cause a fragile filter material to tear away from the central piercing point, with the result that the filter disk remains attached to the well at a portion of the disk periphery.
A probe tip apparatus for removing liquid from a sealed vial is disclosed in U.S. Pat. No. 4,862,753. The probe tip includes exposed cutting surfaces for cutting a seal on the vial and a probe centrally located within the cutting edges for removing liquid from the vial by suction.
Accordingly, it would be desirable to provide a means for removing retentate and filter paper from a multi-well filtration plate which assures that the filter paper will be completely removed from the well without loss of a portion of the retentate for purposes of subsequent testing. Furthermore, it would be desirable to provide such a means which permits removal of the filter and retentate from a plurality of wells simultaneously.